Rapid Thermal Processing (RTP) is employed in many industries where heating of a product at some point in time during production is required. One such product, for example, involves semiconductors in semiconductor chip manufacturing. In such processes a heating method (e.g., an optical heating method) is used to ramp up the temperature of a semiconductor wafer rapidly, hold at a steady state high temperature for a period of time, and then ramp down rapidly. RTP allows the wafer to be heated very quickly to its activation temperatures (e.g., at least 1000 degrees C.). The activation temperature is the temperature at which a corresponding processing step (e.g., deposition, implantation, diffusion, removal or formation of key materials) is stabilized. The temperature and the period of time at which that temperature is maintained must be executed precisely for each processing step. Overheating can cause dopants to permeate subjacent layers, and under-heating can produce layers with uncontrolled characteristics.
RTP in semiconductor processing has been used for annealing of semiconductor wafers. One such application of RTP is to anneal the wafer after ion implantation. The RTP heaters used for these purposes must have a high uniformity; that is, the temperature must be uniform across the entire wafer surface. In most known RTP heaters, the solid angle of the filament—which is the solid angle subtended by the filament when viewed from the wafer surface—is extremely small, on the order of a tenth of a radian. The view factor area then is defined as the area projected on the wafer by the solid angle of the filament (i.e., the solid angle of the filament multiplied by the distance between the filament and the wafer). When the total solid angle for the total wafer coverage is 4.pi. radians, a solid angle of a tenth of a radian covers only about 1% of the wafer. Reflectors outside a container wall of quartz only extend the radiation field for the short wavelength radiation field.
Known RTP heaters have a relatively short lifetime because those lamps have a physical connection between their filaments and their power supplies. Such lamps are sealed on the ends, and the wires connecting the filaments are brought to the outside world to be physically connected to a power supply. This physical connection causes a high failure rate due to the filament input/output connection failure, which in turn is due to the stresses built up at the interface as a result of the different thermal expansion rates of the metals in the connection, during normal lamp operation. Known tungsten halogen lamps for use with such systems have used a relatively thin single filament to generate the necessary heat. For example, one such lamp used for many years is a 1000 watt, 240 volt tungsten halogen lamp with a rated life of 150 hours. The lamp has an output of 23,000 lumens with a color temperature of 3200K and a maximum bulb temperature of 900° C.
It would be an advance in the art if the power output and life of such lamp could be increased while reducing the complexity of the lamp and maintaining or lowering the cost.